U.S. patent number 7,813,514 [Application Number 11/414,835] was granted by the patent office on 2010-10-12 for apparatus and method for checking loudspeaker.
This patent grant is currently assigned to Sony Corporation. Invention is credited to Kohei Asada.
United States Patent |
7,813,514 |
Asada |
October 12, 2010 |
Apparatus and method for checking loudspeaker
Abstract
A loudspeaker checking apparatus includes a signal generating
unit configured to generate a test tone signal by adding first and
second sinusoidal signals of different frequencies; a control
circuit configured to allow the signal generating unit to generate
a plurality of test tone signals by varying the frequencies; an
output circuit configured to simultaneously supply the plurality of
test tone signals to a plurality of loudspeakers, respectively; an
analyzing unit configured to perform frequency analysis on an
output signal from a microphone that picks up test tones output
from the plurality of loudspeakers; and a determining unit
configured to determine whether the respective loudspeakers are
normal or abnormal on the basis of an analysis result made by the
analyzing unit.
Inventors: |
Asada; Kohei (Kanagawa,
JP) |
Assignee: |
Sony Corporation
(JP)
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Family
ID: |
37394062 |
Appl.
No.: |
11/414,835 |
Filed: |
May 1, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060251265 A1 |
Nov 9, 2006 |
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Foreign Application Priority Data
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May 9, 2005 [JP] |
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2005-135645 |
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Current U.S.
Class: |
381/58;
700/94 |
Current CPC
Class: |
H04R
29/001 (20130101); H04R 29/002 (20130101) |
Current International
Class: |
H04R
29/00 (20060101) |
Field of
Search: |
;381/56,58,59,300,304,303,307,17,18 ;700/94 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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63-024800 |
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Feb 1988 |
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JP |
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63-048099 |
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Feb 1988 |
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JP |
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62-36188 |
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Aug 1994 |
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JP |
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09-233591 |
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Sep 1997 |
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JP |
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2004-172661 |
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Jun 2004 |
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JP |
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2004-297368 |
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Oct 2004 |
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JP |
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2004-297368 |
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Oct 2004 |
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JP |
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Primary Examiner: Chin; Vivian
Assistant Examiner: Lao; Lun-See
Attorney, Agent or Firm: Lerner, David, Littenberg, Krumholz
& Mentlik, LLP
Claims
The invention claimed is:
1. A loudspeaker checking apparatus comprising: a signal generating
unit configured to generate a test tone signal by adding first and
second sinusoidal signals of different frequencies; a control
circuit configured to allow the signal generating unit to generate
a plurality of test tone signals by varying the frequencies; an
output circuit configured to simultaneously supply the plurality of
test tone signals to a plurality of loudspeakers, respectively; an
analyzing unit configured to perform frequency analysis on an
output signal from a microphone that picks up test tones output
from the plurality of loudspeakers; and a determining unit
configured to determine whether the respective loudspeakers are
normal or abnormal on the basis of an analysis result made by the
analyzing unit, wherein the signal generating unit includes: a
memory storing digital data representing one cycle of a sinusoidal
signal; a first generating unit configured to generate the first
sinusoidal signal having a frequency x times that of the sinusoidal
signal by reading the digital data from the memory every x samples,
x being a natural number; a second generating unit configured to
generate the second sinusoidal signal having a frequency y times
that of the sinusoidal signal by reading the digital data from the
memory every y samples, y being a natural number different from x;
and an adding circuit configured to add the first and second
sinusoidal signals so as to generate the test tone signal.
2. The loudspeaker checking apparatus according to claim 1, wherein
the analyzing unit performs frequency analysis on dark noise by
using an output signal from the microphone before the test tones
are output from the plurality of loudspeakers and allows the output
circuit to output the test tone signals if the level of the dark
noise is lower than a predetermined value.
3. The loudspeaker checking apparatus according to claim 1,
wherein, if the determining unit determines that at least one of
the loudspeakers has not output the test tone, the control circuit
performs control so that the frequency analysis and the
determination are performed again under different frequencies of
the first and second sinusoidal signals.
4. A loudspeaker checking method comprising the steps of:
generating a test tone signal by adding first and second sinusoidal
signals of different frequencies; generating a plurality of test
tone signals by varying the frequencies; simultaneously supplying
the plurality of test tone signals to a plurality of loudspeakers,
respectively; performing frequency analysis on an output signal
from a microphone that picks up test tones output from the
plurality of loudspeakers; and determining whether the respective
loudspeakers are normal or abnormal on the basis of a result of the
frequency analysis, wherein the step of generating a test tone
signal includes the steps of: generating the first sinusoidal
signal having a frequency x times that of a sinusoidal signal by
taking digital data representing one cycle of the sinusoidal signal
every x samples, x being a natural number; generating the second
sinusoidal signal having a frequency y times that of the sinusoidal
signal by taking the digital data every y samples, y being a
natural number different from x; and adding the first and second
sinusoidal signals so as to generate the test tone signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority from Japanese Patent
Application No. JP 2005-135645, filed on May 9, 2005, the
disclosure of which is hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and a method for
checking loudspeakers of a playback apparatus.
A loudspeaker array is favorably used as a loudspeaker system in a
home theater or an AV system. FIG. 13 shows an example of a
loudspeaker array 10, which includes many loudspeakers SP1 to SPm
arranged (loudspeaker unit). In this loudspeaker array 10, m=256
and the diameter of each loudspeaker is several centimeters, for
example. Therefore, the loudspeakers SP1 to SPm are actually
two-dimensionally arranged on a plane surface. However, the
following description is given under the assumption that the
loudspeakers SP1 to SPm are aligned in the horizontal direction for
convenience.
Audio signals are supplied from a signal source SS to delay
circuits DL1 to DLm, where the audio signals are delayed by
predetermined times .tau.1 to .tau.m, respectively, and the delayed
audio signals are supplied to the loudspeakers SP1 to SPm through
power amplifiers PA1 to PAm. The delay times .tau.1 to .tau.m used
in the delay circuits DL1 to DLm are described below.
Then, sound waves output from the loudspeakers SP1 to SPm are
synthesized and a sound pressure as a synthesis result is obtained
at any point. As shown in FIG. 13, in a sound field generated by
the loudspeakers SP1 to SPm, predetermined points Ptg and Pnc are
defined as follows:
Ptg: a point where the sound pressure is higher than that of any
other points, that is, a point of enhanced sound pressure; and
Pnc: a point where the sound pressure is lower than that of any
other points, that is, a point of reduced sound pressure.
In this case, a method illustrated in FIG. 14 or 15 can be mainly
used as a method for making an arbitrary point the point of
enhanced sound pressure Ptg.
That is, in the method illustrated in FIG. 14, assume that L1 to
Lm: respective distances from the loudspeakers SP1 to SPm to the
point of enhanced sound pressure Ptg; and that s: sound
velocity.
The delay times .tau.1 to .tau.m of the delay circuits DL1 to DLm
are set as follows: .tau.1=(Lm-L1)/s; .tau.2=(Lm-L2)/s;
.tau.3=(Lm-L3)/s; . . . and .tau.m=(Lm-Lm)/s=0.
In this method, when the audio signals output from the signal
source SS are converted to sound waves by the loudspeakers SP1 to
SPm and are output therefrom, those sound waves are output while
being delayed by the times .tau.1 to .tau.m, respectively. Thus,
all of those sound waves reach the point of enhanced sound pressure
Ptg at the same time, so that the sound pressure at the point Ptg
is higher than that of any other points.
In other words, in the method illustrated in FIG. 14, time
differences occur among the sound waves due to variations in the
paths from the loudspeakers SP1 to SPm to the point of enhanced
sound pressure Ptg. However, the delay circuits DL1 to DLm
compensate for the time differences so that the sound waves focus
on the point of enhanced sound pressure Ptg.
In the method illustrated in FIG. 15, the delay times .tau.1 to
.tau.m of the delay circuits DL1 to DLm are set so that the phase
wavefronts of progressive waves (sound waves) output from the
loudspeakers SP1 to SPm match with each other. Accordingly,
directivity is given to the sound waves and the sound waves are
directed to the point of enhanced sound pressure Ptg. This system
corresponds to the focus-type system shown in FIG. 14 in which the
distances L1 to Lm are changed to infinite.
The following Patent Documents are cited as known arts: Patent
Document 1 (Japanese Unexamined Patent Application Publication No.
9-233591) and Patent Document 2 (Japanese Unexamined Patent
Application Publication No. 2004-172661).
SUMMARY OF THE INVENTION
As described above, the point of enhanced sound pressure Ptg can be
freely set by using the loudspeaker array 10. However, the number
of loudspeakers SP1 to SPm included in the loudspeaker array 10 is
several tens to several hundred, and those loudspeakers SP1 to SPm
operate at almost the same time during playback.
Thus, even if a failure occurs in any of the loudspeakers, for
example, even if poor connection or disconnection of a voice coil
occurs, the failure may not be detected. Furthermore, much time is
required to specify or determine the broken loudspeaker.
The present invention has been made in view of these circumstances,
and is directed to enabling quick and accurate check
(determination) of whether each loudspeaker has a failure in a
system using many loudspeakers, such as a loudspeaker array.
According to an embodiment of the present invention, a test tone
signal is generated by adding first and second sinusoidal signals
of different frequencies; a plurality of test tone signals are
generated by varying the frequencies; the plurality of test tone
signals are simultaneously supplied to a plurality of loudspeakers,
respectively; frequency analysis is performed on an output signal
from a microphone that picks up test tones output from the
plurality of loudspeakers; and whether the respective loudspeakers
are normal or abnormal is determined on the basis of a result of
the frequency analysis.
With this configuration, whether the respective loudspeakers have a
failure can be swiftly checked. Since the test tone contains a
plurality of frequency components, the check can be accurately
performed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a waveform diagram illustrating an embodiment of the
present invention;
FIG. 2 shows an example of a tone frequency list;
FIG. 3 shows an example of a tone sequence list;
FIG. 4 is a timing chart illustrating an embodiment of the present
invention;
FIGS. 5A and 5B show frequency spectrums according to an embodiment
of the present invention;
FIG. 6 is a systematic diagram showing a sound-field correcting
apparatus according to an embodiment of the present invention;
FIG. 7 is a flowchart of a routine performed by the apparatus shown
in FIG. 6;
FIG. 8 is a flowchart showing the details of part of the routine
shown in FIG. 7;
FIG. 9 is a flowchart of a routine performed by the apparatus shown
in FIG. 6;
FIG. 10 is a systematic diagram showing part of the apparatus shown
in FIG. 6;
FIG. 11 shows another example of the tone frequency list;
FIG. 12 shows another example of the tone sequence list;
FIG. 13 shows an example of a known loudspeaker array;
FIG. 14 illustrates a method for making an arbitrary point a point
of enhanced sound pressure; and
FIG. 15 illustrates another method for making an arbitrary point a
point of enhanced sound pressure.
DETAILED DESCRIPTION
<1> Outline of the Present Invention
In an embodiment of the present invention, test tone signals STT,
each generated by mixing at least two sinusoidal signals Sa and Sb,
are supplied to loudspeakers SP1 to SPm. The frequencies of the
sinusoidal signals Sa and Sb in the respective test tone signals
STT are different in the respective loudspeakers.
Then, test tones having frequency components corresponding to the
test tone signals STT are output from the loudspeakers SP1 to SPm,
and frequency analysis is performed on the output test tones. If a
predetermined frequency component can be obtained, the loudspeaker
that has output a test tone of the frequency component is
determined to be normal. If the predetermined frequency component
cannot be obtained, the loudspeaker that has output a test tone of
the frequency component is determined to be abnormal. In this way,
whether each loudspeaker has a failure is determined on the basis
of a frequency component obtained through frequency analysis.
<2> Sinusoidal Signal
Assume that, as shown in A in FIG. 1, digital data DD, which is to
be D/A (digital to analog) converted to one cycle of a sinusoidal
signal S1, is stored in a memory. In this case, the digital data DD
corresponds to data that is obtained by sampling one cycle of the
sinusoidal signal S1 into N samples, and thus one cycle is composed
of N samples. Also, assume that N=power of 2 . . . (1), for
example, N=4096.
The respective samples of the digital data DD are written in 0-th
address to (N-1)-th address of the memory in a normal order. The
digital data DD may be data of a typical format in digital audio,
that is, data having a quantifying bit number of 16 bits and in a
format of two's-complement numbers.
Additionally, assume that
fS: clock frequency used to read the data DD from the memory;
f1: the frequency of the sinusoidal signal S1, f1=fs/N; and
TN: one cycle of the sinusoidal signal S1, TN=1/f1.
Under this condition, if fs=48 (kHz),
.times..times..apprxeq..times. ##EQU00001##
Accordingly, if the digital data DD is sequentially read one sample
by one from the respective addresses of the memory with the clock
frequency fS, one cycle of a sinusoidal signal S1 having a
frequency of 11.72 Hz (=f1) can be obtained in the time TN, as
indicated as "a=1" in B in FIG. 1.
If the digital data DD is read from the memory every other address
and if the reading is repeated twice, two cycles of a sinusoidal
signal S2 having a double frequency 2f1 (=23.44 Hz) can be obtained
in the time TN, as indicated as "a=2" in B in FIG. 1.
If the digital data DD is read from the memory every three
addresses and if the reading is repeated three times, three cycles
of a sinusoidal signal S3 having a triple frequency 3f1 (=35.16 Hz)
can be obtained in the time TN, as indicated as "a=3" in B in FIG.
1.
Likewise, if the digital data DD is read from the memory every "a"
addresses ("a" is a natural number) and if the reading is repeated
"a" times, "a" cycles of a sinusoidal signal Sa having an a-fold
frequency af1 can be obtained in the time TN.
Thus, if
fa: frequency of a sinusoidal signal Sa obtained in the time TN,
fa=f1.times.a=fS/N.times.a . . . (3) is satisfied on the basis of
expression (2). A sinusoidal signal Sb having a frequency fb can be
generated in the same way.
As in the above-described case where "a" cycles of the sinusoidal
signal Sa are just included within the time TN, if frequency
analysis is performed by FFT (Fast Fourier Transform) on the
sinusoidal signal Sa, amplitude occurs only at the frequency fa of
the sinusoidal signal Sa, and amplitude does not occur at any other
frequencies. This is the same for the sinusoidal signal Sb.
Therefore, when a test tone output from a loudspeaker to be checked
is picked up to obtain sinusoidal signals Sa and Sb and when
frequency analysis is performed on these signals Sa and Sb,
window-function processing need not be performed, so that the
frequency analysis can be easily performed.
Further, since the number N of samples in the memory is defined by
expression (1), the memory can be efficiently used. For example,
one cycle of the digital data DD can be obtained and the memory can
be saved by reading the digital data DD in the following manner.
The first 1/4 cycle of the digital data DD is prepared in the
memory. During reading of the digital data DD, the data is read in
the normal order of address in the first 1/4 cycle, the data is
read in the reverse order in the second 1/4 cycle, the data is read
in the same manner in the third and fourth 1/4 cycles, and then the
polarity of the read data is inverted. Alternatively, the digital
data DD can be data sequence of a cosine wave signal instead of the
sinusoidal signal S1.
In the following description, the above-described specific values
N=4096 and fS=48 kHz are used.
<3> Tone Frequency List
A "tone frequency list" is a list (or table) to define the
frequencies of sinusoidal signals Sa and Sb included in respective
test tone signals STT. FIG. 2 shows an example of the tone
frequency list. In the list shown in FIG. 2, 128 types of test tone
signals STT can be used.
In this tone frequency list, a first column shows pattern numbers
PN to identify the respective 128 types of test tone signals STT.
In this example, PN=1 to 128. Second and third columns show
frequencies a and b of sinusoidal signals Sa and Sb included in the
respective test tone signals STT.
For example, in the row of PN=1, a=100 and b=740. Thus, the test
tone signal STT of PN=1 is composed of sinusoidal signals S100 and
S740. At this time, the frequencies f100 and f740 of the sinusoidal
signals S100 and S740 can be defined in the following expressions
based on expression (3): f100=48000/4096.times.100.apprxeq.1171.9
(Hz); and f740=48000/4096.times.740.apprxeq.8671.9 (Hz).
The test tone signal STT of PN=128 is composed of sinusoidal
signals S735 and S1375. At this time, the frequencies f735 and
f1375 can be defined in the following expressions:
f735=48000/4096.times.735.apprxeq.8623.3 (Hz); and
f1375=48000/4096.times.1375.apprxeq.16113.3 (Hz).
As can be understood from this tone frequency list, the frequencies
fa and fb of sinusoidal signals Sa and Sb are different in the
respective test tone signals STT.
<4> Tone Sequence List
A "tone sequence list" is a list (or table) showing the
correspondence between the loudspeakers SP1 to SPm and the pattern
numbers PN of the test tone signals STT supplied thereto. FIG. 3
shows an example of the tone sequence list. In the list shown in
FIG. 3, the number of loudspeakers SP1 to SPm is 128 (m=128).
In this case, 128 types (PN=1 to 128) of test tone signals STT are
simultaneously supplied to the 128 loudspeakers SP1 to SP128 so
that a failure in the loudspeakers SP1 to SP128 can be checked in a
short time.
Note that, a frequency characteristic of loudspeakers typically has
a peak and a dip. Due to the dip, a loudspeaker supplied with a
test tone signal STT may not output a predetermined test tone, and
thus a test tone may not be picked up. This phenomenon may be
misinterpreted as a failure of the loudspeaker.
In view of such inconvenience, the test tone signals STT are
supplied to the loudspeakers SP1 to SP128 three times in the tone
sequence list shown in FIG. 3. More specifically, in the tone
sequence list shown in FIG. 3, a first column shows loudspeaker
numbers SN assigned to the loudspeakers SP1 to SPm. In this
example, m=128 and thus SN=1 to 128. Second to fourth columns show
pattern numbers PN of the test tone signals STT to be supplied to
the loudspeakers SP1 to SP128 at the first time (SEQ=1) to the
third time (SEQ=3), respectively.
At the first supply, the test tone signals STT of PN=1 to 128 are
simultaneously supplied to the loudspeakers SP1 to SP128, as shown
in the column "FIRST" in FIG. 3. At the second supply, the test
tone signals STT of PN=33 to 128 and PN=1 to 32 are simultaneously
supplied to the loudspeakers SP1 to SP96 and SP97 to SP128, as
shown in the column "SECOND" in FIG. 3. At the third supply, the
test tone signals STT of PN=65 to 128 and PN=1 to 64 are
simultaneously supplied to the loudspeakers SP1 to SP64 and SP65 to
SP128, as shown in the column "THIRD" in FIG. 3.
In this method, the frequency components of the test tone signals
STT supplied to the loudspeakers SP1 to SP128 are different from
each other, and thus the frequency components of test tones output
from the loudspeakers SP1 to SP128 are different from each other.
Therefore, whether the respective loudspeakers SP1 to SP128 have a
failure can be determined by performing frequency analysis on test
tones output from the loudspeakers SP1 to SP128 and checking
frequency components as the analysis result.
Since the test tone signals STT are simultaneously supplied to the
128 loudspeakers SP1 to SP128, whether the respective loudspeakers
SP1 to SP128 have a failure can be checked in a short time.
Further, as shown in FIG. 3, check is repeatedly performed as
necessary and the frequency components of the test tone signals STT
supplied to the loudspeakers SP1 to SP128 are changed in each
check. Thus, whether the respective loudspeakers have a failure can
be accurately checked even if the frequency characteristic of the
loudspeakers SP1 to SP128 has a dip.
<5> Format of Test Tone Signal STT
"A" in FIG. 4 shows a format (timing chart) of one channel of a
test tone signal STT. The test tone signal STT is generated and is
supplied to a predetermined loudspeaker during a test time TT. The
test time TT is composed of a silent time TS, a readiness time TR,
a check time TC, and an end time TE.
Herein, the silent time TS is a time for measuring dark noise
(background noise) of a room where the loudspeakers SP1 to SPm are
set, and a test tone signal STT is idle during this time. The
readiness time TR is a time for setting an appropriate volume of a
test tone to be output from each loudspeaker during the following
check time TC. The check time TC is a time for actually checking
whether the loudspeakers SP1 to SPm have a failure. The end time TE
is a time used to end the test tone and is not used to check
whether the loudspeakers have a failure.
In A of FIG. 4, each of the times TS, TR, TC, and TE is composed of
a single unit time TU. Note that, the check time TC is basically
composed of a single unit time TU but is composed of two or three
unit times TU when check of the loudspeakers SP1 to SPm is
repeated, as shown in B and C in FIG. 4.
As shown in D in FIG. 4 (the time axis is extended in D, E, and F
of FIG. 4), the unit time TU is equal to 2.times.TN shown in FIG.
1. When a plurality of test tone signals STT are simultaneously
supplied to the loudspeakers SP1 to SPm, the content thereof is
changed in the unit time TU.
Herein, the test tone signal STT is a composite signal composed of
sinusoidal signals Sa and Sb, as described above. Since the numbers
a and b of cycles of the signals Sa and Sb in the time TN are
natural numbers, the phase of the test tone signal STT smoothly
changes at the border between the times TN and TN in the unit time
TU.
In the case of the above-described values,
TU=TN.times.2=4096/48000.times.2.apprxeq.171 (msec).
In the case of A in FIG. 4, TT=TS+TR+TC+TE=TU.times.4,683
(msec).
When such a test tone signal STT is supplied to a loudspeaker to be
checked, the loudspeaker outputs a test tone having a frequency
component corresponding to the test tone signal STT if the
loudspeaker is normal.
After the test tone output from the loudspeaker is picked up by a
microphone, the microphone outputs a test tone signal STT as shown
in E in FIG. 4 (hereinafter, the test tone signal STT output from
the microphone is called a "response signal STT"). The response
signal STT delays by time .tau. with respect to the test tone
signal STT (D in FIG. 4) supplied to the loudspeaker, the time
.tau. corresponding to the distance between the loudspeaker and the
microphone.
Thus, as shown in F in FIG. 4, whether the loudspeaker has a
failure can be checked by performing frequency analysis on the
response signal STT from the microphone over a predetermined time
TA.
As shown in E in FIG. 4, in the response signal STT from the
microphone, the same content is repeated twice during the times TN
and TN in the unit time TU, and thus the time position of the
analysis time TA has a sufficient allowance. Therefore, after the
response signal STT has been output from the microphone, frequency
analysis of the response signal STT can be started with the rising
edge of the output signal being the reference of the check time TC,
and thus the delay time .tau. of the picked up response signal STT
need not be considered so much.
Since the test tone signal STT is a composite signal composed of
sinusoidal signals Sa and Sb, the number of cycles of the response
signal STT in the analysis time TA is an integer if the analysis
time TA is equal to TN. Therefore, window-function processing need
not be performed in frequency analysis, so that the frequency
analysis can be simplified.
If no test tone is output from a loudspeaker during the check time
TC (=TU) shown in A in FIG. 4, the check time TC is extended as
shown in B or C in FIG. 4, and the frequencies of the sinusoidal
signals Sa and Sb in the test tone signal STT supplied to the
loudspeaker are changed as shown in FIG. 3. In this method, if no
test tone is output from a loudspeaker, the cause can be correctly
determined: due to a failure of the loudspeaker or a dip of the
frequency characteristic. Accordingly, whether the respective
loudspeakers have a failure can be reliably determined.
<6> Method for Determining Dark Noise (Background Noise) and
Failure in Loudspeakers
As shown in FIG. 4, the silent time TS at the top of the test time
TT is used to avoid an affection of dark noise on checking failure
of the loudspeakers. When test tones output from the loudspeakers
are picked up and a response signal STT obtained thereby is
analyzed in order to measure the levels of respective frequency
components of the test tones, the analysis result (frequency
components) contains frequency components of dark noise.
For this reason, frequency components of dark noise need to be
considered when a failure of the loudspeakers is determined on the
basis of the analysis result of the test tones. Hereinafter, an
example of a determining method considering dark noise is
described.
First, dark noise in the silent time TS is picked up and frequency
analysis is performed thereon. As shown in FIG. 5B, for example,
the levels of respective frequency components (noise components)
are obtained and the levels are stored. At this time, only the
levels of components having the same frequencies as those of the
sinusoidal signals Sa and Sb in the test tone signal STT are to be
stored. The levels of the other frequency components need not be
stored. The frequencies of the sinusoidal signals Sa and Sb can be
known by referring to the tone frequency list.
Then, in the check time TC, the test tone signal STT is supplied to
the loudspeaker to be checked, frequency analysis is performed on a
response signal STT output from the loudspeaker, and the levels of
respective frequency components are obtained, as shown in FIG. 5A.
In FIG. 5A, the signals Sa and Sb are frequency components obtained
from the loudspeaker to be checked, and the other frequency
components are caused by dark noise. Typically, the levels of the
signals Sa and Sb vary depending on the frequency characteristic of
a loudspeaker, and the signals Sa and Sb contain frequency
components of dark noise.
Then, the S/N (signal to noise) ratio between the signal Sa and a
noise component Na having a frequency equal to that of the signal
Sa among the noise components whose levels are stored (FIG. 5B) is
calculated, and the S/N ratio is regarded as a value Va. Also, the
S/N ratio between the signal Sb and a noise component Nb having a
frequency equal to that of the signal Sb among the noise components
is calculated, and the S/N ratio is regarded as a value Vb. If the
level of any of the signals Sa and Sb does not reach a
predetermined value VTH, the S/N ratio is not calculated and the
corresponding value is set to 0.
In the values Va and Vb, a value Vx (x is one of a and b) having
the higher S/N ratio is selected, and this maximum value Vx is
compared with a predetermined value VREF. Then, determination is
made in the following manner:
(i) if Vx>VREF, the checked loudspeaker is normal; and
(ii) if Vx.ltoreq.VREF, the checked loudspeaker has a failure.
In this way, whether the loudspeaker has a failure is determined by
comparing the predetermined value VREF with the S/N ratio of a
signal having the most favorable S/N ratio among the signals Sa and
Sb in the picked up response signal STT. Therefore, the
determination can be accurately made while avoiding the affection
of the frequency characteristic of the loudspeaker or the
standing-wave characteristic of a room.
<7> Sound-Field Correcting Apparatus
FIG. 6 shows an example in which the present invention is applied
to a sound-field correcting apparatus. In this example, m=128.
<7-1> Configuration and Operation of the Sound-Field
Correcting Apparatus
Digital audio signals DA are output from a signal source SS of a
DVD player, a digital tuner, or a game machine, and the digital
audio signals DA are supplied to digital filters 221 to 22m (m=128)
through an input terminal 21.
The format of each digital audio signal DA is the same as that of
the digital data DD of the sinusoidal signal S1. The digital
filters 221 to 22m perform a delay process as the delay circuits
DL1 to DLm shown in FIG. 13 and also perform sound-field correction
as necessary. Accordingly, digital audio signals to generate the
point of enhanced sound pressure Ptg as shown in FIG. 14 or 15 are
output from the digital filters 221 to 22m.
Then, the digital audio signals are supplied to digital amplifiers
241 to 24m through switching circuits 231 to 23m. In this example,
the digital amplifiers 241 to 24m are so-called class D amplifiers,
and perform class D power amplification on the supplied digital
audio signals by switching so as to output analog audio signals of
respective channels.
Then, the audio signals output from the digital amplifiers 241 to
24m are supplied to loudspeakers SP1 to SPm, respectively. In this
example, the loudspeakers SP1 to SPm form the loudspeaker array 10,
as described above. For example, the loudspeakers are arranged in
line as shown in FIG. 13 or in rows.times.columns in front of a
listener. Although not shown in the figure, the loudspeakers SP1 to
SPm are accommodated in a cabinet.
Further, a control circuit 25 is provided. The control circuit 25
includes a microcomputer and sets delay times .tau.1 to .tau.m in
accordance with the point of enhanced sound pressure Ptg (or the
point of reduced sound pressure Pnc), the delay times .tau.1 to
.tau.m being used by the digital filters 221 to 22m to delay
digital audio signals DA. Thus, control signals to control the
delay times .tau.1 to .tau.m are supplied from the control circuit
25 to the digital filters 221 to 22m.
Also, control signals are supplied from the control circuit 25 to
the switching circuits 231 to 23m. The switching circuits 231 to
23m are connected in the manner shown in FIG. 6 during a normal
playback, but are connected in the opposite manner while a failure
of the loudspeakers SP1 to SPm is being checked. Further, various
operation switches 26 are connected to the control circuit 25.
With this configuration, digital audio signals DA from the signal
source SS are supplied to the loudspeakers SP1 to SPm through
signal lines including the digital filters 221 to 22m; the
switching circuits 231 to 23m; and the digital amplifiers 241 to
24m, during a normal playback. At this time, the predetermined
delay times .tau.1 to .tau.m are given to the digital audio signals
DA in the digital filters 221 to 22m, so that the point of enhanced
sound pressure Ptg is generated and the position thereof is
controlled.
<7-2> Configuration for Checking Failure in Loudspeakers
Whether the loudspeakers SP1 to SPm have a failure is checked in
the following configuration. A signal generating circuit 31 to
generate test tone signals STT includes a digital signal processor
(DSP) or the like. Control signals to control the frequencies fa
and fb of the sinusoidal signals Sa and Sb in the respective test
tone signals STT are supplied from the control circuit 25 to the
signal generating circuit 31.
The control circuit 25 performs frequency analysis on test tones
output from the loudspeakers SP1 to SPm during the above-described
analysis time TA and determines a failure in the loudspeakers SP1
to SPm in accordance with the analysis result. For this purpose,
the control circuit 25 has routines 100, 200, and 300 shown in
FIGS. 7 to 9, which are programs executed by the microcomputer in
the control circuit 25.
These routines 100 to 300 are described below in detail. FIGS. 7 to
9 show the part related to the present invention. After test tone
signals STT are generated by the signal generating circuit 31 under
control by the control circuit 25, the test tone signals STT are
supplied to the switching circuits 231 to 23m and the switching
circuits 231 to 23m are connected to the signal generating circuit
31.
A microphone 32 picks up test tones output from the loudspeakers
SP1 to SPm. A response signal STT output from the microphone 32 is
supplied through a microphone amplifier 33 to an A/D (analog to
digital) converter 34, which A/D converts the response signal STT
to a digital response signal STT, and the digital response signal
STT is supplied to the control circuit 25.
The microphone 32 can be provided in the cabinet which accommodates
the loudspeakers SP1 to SPm. The control circuit 25 connects to a
LCD (liquid crystal display) panel 35, which is a display device to
display a determination result of a failure in the loudspeakers SP1
to SPm.
<7-3> Operation of Checking Failure in Loudspeakers
Upon operation on a check switch among the operation switches 26,
the microcomputer included in the control circuit 25 starts the
routine 100 from step 101. Initial setting is done in step 102, so
that the switching circuits 231 to 23m are connected in the manner
opposite to that shown in the FIG. 6. Also, generation of test tone
signals STT starts and a test time TT starts.
In the test time TT, the levels of dark noise in a silent time TS
are measured in steps 111 to 114. That is, dark noise is picked up
by the microphone 32, and a signal of the picked up dark noise is
supplied to the control circuit 25 through the amplifier 33 and the
A/D converter 34.
In step 111, frequency analysis based on FFT is performed on the
signal of the dark noise (FIG. 5B), and the levels of respective
frequency components of the dark noise are stored. The levels
stored at this time are those of components having frequencies
equal to those of the signals Sa and Sb in the test tone signal
STT. The frequencies of the signals Sa and Sb can be referred to in
the tone frequency list (FIG. 2).
Then, in step 112, the levels of the frequency components analyzed
and stored in step 111 are compared with a predetermined noise
level.
In step 113, the comparison result made in step 112 is checked. If
all of the noise levels are lower than the predetermined noise
level, the process proceeds from step 113 to step 114. In step 114,
among the noise levels of the frequency components analyzed in step
111, the noise levels of components whose frequencies are equal to
those of the signals Sa and Sb in the test tone signal STT are
stored in a memory of the control circuit 25.
Then, the process proceeds from step 114 to step 120, where a
process in the readiness time TR is executed. That is, the signal
generating circuit 31 generates test tone signals STT, which are
supplied to the loudspeakers SP1 to SPm through signal lines
including the switching circuits 231 to 23m and the digital
amplifiers 241 to 24m.
The test tone signals STT generated in the readiness time TR are
the test tone signals STT having the pattern numbers PN shown in
FIG. 2. These test tone signals STT can be supplied to the
loudspeakers SP1 to SPm, respectively, in the combination shown in
the column "FIRST" in FIG. 3, for example. Accordingly, test tones
are simultaneously output from the loudspeakers SP1 to SPm during
the readiness time TR.
The test tones output during the readiness time TR are used to
adequately set the output levels of the loudspeakers SP1 to SPm in
the following check time TC. Thus, the levels of the test tones are
relatively low but can be set while considering the analysis result
of the dark noise in the previous silent time TS. Further, the test
tones output in the readiness time TR are picked up by the
microphone 32, a response signal STT corresponding to the picked up
test tone is supplied to the control circuit 25, and then the
levels of the test tone signals STT used in the following check
time TC are set.
Then, in step 130, a process in the check time TC is executed, as
described below. Then, in step 140, a process in the end time TE is
executed. That is, test tone signals STT for end are generated by
the signal generating circuit 31 under control by the control
circuit 25, and these signals STT are supplied to the loudspeakers
SP1 to SPm.
Then, in step 151, generation of test tone signals STT ends, the
switching circuits 231 to 23m are connected in the manner shown in
FIG. 6, and the test time TT ends. In step 152, the routine 100
completes.
If there is a noise component (frequency component) whose level is
higher than the predetermined noise level in step 113, the process
proceeds from step 113 to step 116, where whether the number of
measurements of dark noise levels (measurements in the silent time
TS) has reached a predetermined number is checked. If the number
has not reached the predetermined number, the process returns to
step 111. Then, the silent time TS is repeated and the levels of
frequency components of dark noise are measured again in the
following steps.
If the number of measurements has reached the predetermined number
in step 116, the process proceeds to step 117, where instructions
to improve the environment and reduce dark noise is displayed in
the LCD panel 35. Then, the process proceeds to step 152 through
step 140, so that the routine 100 completes.
The process in the check time TC in step 130 is executed in the
manner shown in the routine 200 in FIG. 8. Specifically, in the
check time TC, the microcomputer included in the control circuit 25
starts the routine 200 from step 201. In step 202, a variable SEQ
indicating any of "FIRST" to "THIRD" of the tone sequence list
shown in FIG. 3 is set to 1.
In step 203, test tone signals STT having the pattern numbers PN
shown in FIG. 2 are generated in accordance with the combination
shown in the column indicated by the variable SEQ (the column
"FIRST" in this case) of the tone sequence list shown in FIG. 3,
and these signals STT are simultaneously supplied to the
loudspeakers SP1 to SPm. Accordingly, test tones are output from
the loudspeakers SP1 to SPm during the check time TC.
The test tones are picked up by the microphone 32, a response
signal STT to the test tones is supplied to the control circuit 25,
and frequency analysis is performed on the response signal STT
during the above-described analysis time TA. Based on the analysis
result, whether the respective loudspeakers SP1 to SPm have a
failure is determined. The frequency analysis and determination of
failure in the respective loudspeakers SP1 to SPm are executed in
accordance with the routine 300.
Then, the determination result made in the routine 300 is checked
in step 204. If all of the loudspeakers SP1 to SPm are normal, the
process proceeds from step 204 to step 205, where a message saying
that all of the loudspeakers SP1 to SPm are normal is displayed on
the LCD panel 35. Then, the routine 200 completes in step 209, and
the process proceeds to step 140 of the routine 100.
If it is determined in step 204 that any of the loudspeakers SP1 to
SPm has not output a test tone, the process proceeds from step 204
to step 206, where the variable SEQ is incremented by one. Then, in
step 207, it is determined whether the variable SEQ is 4 or
more.
If the variable SEQ is less than 4, the process returns from step
207 to step 203, and the subsequent steps are repeated. In other
words, the check time TC is repeated.
Note that, since the variable SEQ is incremented every time step
206 is executed, the combination of the test tone signals STT
having the pattern numbers PN shown in FIG. 2 is changed to that
shown in the column "SECOND" or "THIRD" in the tone sequence list
shown in FIG. 3 every time step 203 and thereafter are repeated.
Accordingly, the loudspeakers SP1 to SPm output test tones of
different frequency components in each check time TC.
After a second or third check has been done, if all of the
loudspeakers SP1 to SPm are determined to be normal, the process
proceeds from step 204 to step 205, where a message saying that all
of the loudspeakers SP1 to SPm are normal is displayed on the LCD
panel 35. Then, the routine 200 completes in step 209, and the
process proceeds to step 140 of the routine 100.
If any of the loudspeakers SP1 to SPm does not output a test tone
at the third check, the process proceeds to step 206. Since
SEQ.gtoreq.4, the process proceeds from step 207 to step 208, where
the loudspeaker number of an abnormal loudspeaker is displayed on
the LCD panel 35. Then, the routine 200 completes in step 209, and
the process proceeds to step 140 of the routine 100.
In addition to the above-described process, the control circuit 25
executes the routine 300 in parallel with the routine 100 during
the analysis time TA so as to determine failure in the respective
loudspeakers SP1 to SPm. In the routine 300, the process starts
from step 301. In step 302, a response signal STT output from the
A/D converter 34 is input to the control circuit 25 and frequency
analysis is performed thereon in the analysis time TA. Then,
frequency components analyzed in step 302 are separated for the
corresponding loudspeakers in step 303. This separation is
performed while the tone frequency list and the tone sequence list
are referred to.
In step 304, the loudspeaker number SN (FIG. 3) is set to "1"
corresponding to the first loudspeaker SP1, and a "failure list" is
generated. The failure list shows information about whether the
respective loudspeakers SP1 to SPm have a failure. In step 304, the
status of all of the loudspeakers SP1 to SPm is temporarily set to
"failure".
In step 305, the levels of the frequency components separated from
each other in step 303 are compared with the levels of the noise
components stored in the memory in step 114 of the routine 100. In
this comparison, the levels of signals Sa and Sb included in a test
tone signal STT supplied to the loudspeaker indicated by the
loudspeaker number SN are compared with the levels of noise
components Na and Nb whose frequencies are equal to those of the
signals Sa and Sb (FIG. 5). The frequencies of the signals Sa and
Sb to be compared can be known on the basis of the loudspeaker
number SN, the variable SEQ, and the pattern number PN (FIG.
3).
If the comparison result is the above-described (i), the process
proceeds from step 305 to step 306, where the status of the
loudspeaker indicated by the loudspeaker number SN is set to
"normal" in the failure list generated in step 304. Then, the
process proceeds to step 307.
If the comparison result obtained in step 305 is (ii), the process
skips to step 307.
In step 307, whether all of the loudspeakers SP1 to SPm have been
checked is determined by referring to the loudspeaker numbers SN.
If a loudspeaker that has not been checked exists, the process
proceeds from step 307 to step 308, where the loudspeaker number SN
is incremented by one and the next loudspeaker is checked. Then,
the process returns to step 305.
In this way, the status of all of the loudspeakers SP1 to SPm is
determined on the basis of the comparison of the levels of the
signals Sa and Sb in the response signal STT, and the information
in the failure list is set to "normal" for a normal
loudspeaker.
After the status of all of the loudspeakers SP1 to SPm has been
determined, the process proceeds from step 307 to step 309, so that
the routine 300 completes.
Incidentally, in step 204 of the routine 200, whether any of the
loudspeakers SP1 to SPm has a failure is determined on the basis of
the failure list updated in step 306. In step 208, the loudspeaker
number SN or the like of a broken loudspeaker is displayed on the
LCD panel 35.
As described above, according to the routines 100 to 300, whether
any of the loudspeakers SP1 to SPm has a failure can be determined
and the determination result can be reported.
<8> Example of the Signal Generating Circuit 31
FIG. 10 shows an example of a configuration of the signal
generating circuit 31 composed of individual circuits. In this
example, a ROM (read only memory) 41 stores digital data DD to be
converted to one cycle of the sinusoidal signal S1 shown in A in
FIG. 1. During the time TN, the digital data DD is read every "a"
addresses of the ROM 41 and the reading is repeated "a" times, so
that a sinusoidal signal Sa is captured and is written in a memory
421a.
During another time TN, the digital data DD stored in the ROM 41 is
read every "b" addresses of the ROM 41 and the reading is repeated
"b" times, so that a sinusoidal signal Sb is captured and is
written in a memory 421b. Therefore, the sinusoidal signals Sa and
Sb are stored in the memories 421a and 421b while being
synchronized.
Then, the signals Sa and Sb in the memories 421a and 421b are
simultaneously read in each time TN, the levels of the read signals
Sa and Sb are adjusted by level adjusting circuits 431a and 431b,
the signals Sa and Sb are supplied to an adder 441 and are added to
a test tone signal STT, and then the test tone signal STT is output
through the switching circuit 231.
Likewise, test tone signals STT for the loudspeakers SP2 to SPm are
generated by memories (422a, 422b) to (42ma, 42mb), level adjusting
circuits (432a, 432b) to (43ma, 43mb), and adders 442 to 44m, and
the generated test tone signals STT are output through the
switching circuits 232 to 23m.
In this way, the test tone signals STT to be supplied to the
loudspeakers SP1 to SPm can be generated. If the signal generating
circuit 31 includes a DSP (digital signal processor) or a CPU
(central processing unit), the process performed in the memories
421a to 42mb and thereafter may be performed on the digital data DD
stored in the ROM 41.
<9> Another Example of the Tone Frequency List and the Tone
Sequence List
FIG. 11 shows another example of the tone frequency list. In this
example, 384 types of test tone signals STT (PN=1 to 384) can be
used. In this tone frequency list, too, frequencies fa and fb of
sinusoidal signals Sa and Sb in the respective test tone signals
STT are different from each other.
FIG. 12 shows another example of the tone sequence list. In the
tone sequence list shown in FIG. 3, the number of the pattern
numbers PN is the same as the number of the loudspeakers SP1 to
SPm, so that the combination of the loudspeaker numbers SN and the
pattern numbers PN is changed in each check. On the other hand, in
the example shown in FIG. 12, all of the pattern numbers PN used in
the first to third checks are different from each other.
<10> Conclusion
According to the above-described checking apparatus, test tone
signals STT of different frequencies are simultaneously supplied to
the loudspeakers SP1 to SPm of the playback apparatus, frequency
analysis is performed on test tones output from the loudspeakers
SP1 to SPm, and a failure in each loudspeaker is determined on the
basis of frequency components corresponding to the loudspeakers SP1
to SPm. In this method, poor connection or disconnection of a voice
coil can be swiftly detected.
Furthermore, check is repeatedly performed by changing the
frequencies of the test tone signals STT as necessary. Therefore,
whether the respective loudspeakers SP1 to SPm have a failure can
be accurately checked even if the frequency characteristic of the
loudspeakers SP1 to SPm has a dip. Also, since each test tone
signal STT is composed of integer cycles of sinusoidal signals Sa
and Sb, frequency analysis of a test tone by FFT can be easily
performed.
<11> Others
In the above-described embodiment, all of the loudspeakers SP1 to
SPm are simultaneously checked. Alternatively, the loudspeakers SP1
to SPm can be divided into a plurality of groups and check can be
performed in units of the groups. Additionally, the terminal 21 to
the amplifiers 241 to 24m can be accommodated together with the
loudspeakers SP1 to SPm in one cabinet.
The present invention can also be applied when a failure of
loudspeakers is checked in a multichannel stereo system, such as a
5.1 channel stereo system, or in a multiway loudspeaker system,
such as a three-way loudspeaker system. The signal generating
circuit 31 can be realized by the microcomputer included in the
control circuit 25. Frequency analysis of a response signal STT can
be performed by a dedicated DSP or CPU.
It should be understood by those skilled in the art that various
modifications, combinations, sub-combinations and alterations may
occur depending on design requirements and other factors insofar as
they are within the scope of the appended claims or the equivalents
thereof.
* * * * *